The airflow meter of an internal combustion (IC) engine measures the combustion airflow into the engine and delivers a corresponding electrical signal to the engine management electronic control unit (ECU). The ECU acts upon this signal to exercise control over certain engine functions, such as fuel delivery and spark timing for example, in accordance with schedules that have been programmed into the ECU.
For any given throttle setting, airflow into the engine may be considered essentially proportional to engine speed, and where the airflow meter is essentially a linear device, the measurement signal provided by the airflow meter is likewise essentially proportional to engine speed. Stated another way, the gain of such an airflow meter is essentially constant for any given throttle setting.
Where an airflow meter is required to have a range that encompasses all operating conditions of the engine, the output signal representing the smallest airflow will occur when the throttle is in idle position and the engine is operating at lowest speed, and the output signal representing the largest airflow will occur when the throttle is wide open and the engine is operating at maximum speed. In typical operation of most automotive vehicles, the concurrence of a high engine speed and of a throttle opening that is at or near wide open happens infrequently, and therefore it is only infrequently that the airflow meter is required to operate at the high end of its range. In other words, most of the time the airflow meter operates over only a limited portion of its range.
The present invention arises through the recognition of this phenomenon and provides an improvement for increasing the gain of the airflow meter at low engine speeds, where greater gain can be especially beneficial, but without altering the range that is required for high-speed, open-throttle operation. While one might be led to intuitively envision the simple addition of a suitable amplification stage to an existing airflow meter for increasing the gain, such an addition will not solve the problem of attaining increased resolution at lower speeds without also having an influence on the range. Moreover, such an addition would also amplify error and jitter, an undesirable side-effect.
In a comprehensive aspect, the present invention comprises means for changing the gain of the airflow meter as a function of engine speed, particularly means to modify the gain as a function of engine speed for any given throttle setting such that over one portion of the engine speed range for said given throttle setting, the gain is different from what it is over another portion of the engine speed range for the same throttle setting. The invention is especially well suited for a hot-wire anemometer type airflow meter.
In some of its more specific aspects the invention comprises: means to cause the gain to be greater for the low end of the engine speed range than it is for the high end; means to change the gain when the engine management ECU detects passage of engine speed through a certain speed; and means to modify the gain by modifying the effective resistance of an arm of a four-sided electrical bridge circuit of the airflow meter.
Other features of the invention, along with additional advantages and benefits, will become apparent upon reading the ensuing description and claims which are accompanied by drawings. The drawings present a currently preferred embodiment of the invention according to the best mode contemplated at this time for putting the invention into practice.